Vehicle alarm systems have become increasingly popular in recent years, particularly with the rising costs of automobiles. Their installation has become standard in more expensive vehicles and is an option on lower price models. The purpose of these systems are to deter theft of vehicles by setting off an alarm when attempts are made to gain unlawful entry into the vehicle. Some set off an alarm by any motion of the vehicle while others are activated merely by proximity sensors that sense a person approaching closely to a protected vehicle.
In some of these alarm systems the alarm is set by the driver when he leaves the vehicle. However, in other systems the alarm is set by a remote control device carried by the driver or owner on his key chain. In either case, when the alarm is set a chirping sound is produced to advise the driver or owner that the alarm has been activated. This chirping sound when setting the alarm can be annoying particularly at nighttime in residential areas. The alarm itself when set off provides a piercing, loud, high frequency sound that usually pulsates. The volume is loud enough to be heard for a considerable distance from the vehicle to draw attention to the fact that someone is tampering with a vehicle.
Because these alarm systems can be an annoyance at quiet times such as nighttime and particularly in residential neighborhoods, devices have been invented to turn off the chirping sound when the alarm is activated. One such device disclosed in U.S. Pat. No. 4,996,515 of Schaffer et al, dated Feb. 26, 1991 automatically suppresses the audible arm and disarm signals associated with these auto alarms. In this system a photo resistor cell is connected to a control circuit to indicate whether the light level is below a threshold level. This distinguishes daytime from nighttime. During the evening or nighttime hours the control circuit suppresses the system signal for a short interval to eliminate the audible chirping arm and disarm signal. Thus in this system the audible alarm is completely eliminated and no feedback is provided to the driver or owner whether the alarm has been set.
It is one object of the present invention to provide a system for controlling the level of the arm/disarm audio signal for an automobile alarm circuit.
Another object of the present invention is to provide an alarm set signal control system that controls not only the level but the period of time that the alarm set signal is to be set for.
Still another object of the present invention is to provide an alarm set signal control system that utilizes a silicon control rectifier to bypass the alarm setting signal to control the volume.